An explosion in the Afghan capital Kabul on Saturday killed at least three people and wounded two in an apparent attack on a foreign contractor company, officials said.

Interior Ministry spokesman Najib Danesh said all those killed and wounded in the explosion were civilians with no casualties among the contractors.

Police officials said the exact cause of the explosion was being investigated and there was no immediate claim of responsibility.

While the latest blast was relatively minor compared with others that have killed scores of people recently, the constant stream of attacks in Kabul has undermined confidence in the Western-backed government of President Ashraf Ghani.

Earlier this week, General John Nicholson, the top U.S. commander in Afghanistan, said security in Kabul would be “the main effort” for international powers helping Afghan defense and security forces.